Control system



fLuE I Aug. 26, 1952 ANALYSER FLUE GAS c. H. sMooT 2,608,351

CONTROL SYSTEM Filed April 28, 195o IN V EN TOR.'

@MMM `inlettcorl,duit I2.

atented Aug. 26; 195.?I

- UNITED Hs'1A'rfEs1 ortica: 2,608,351`v l I y I 'l .A A

CONTROL sYsTE-M Charles HI Sinoot,v Chicago, Ill'.. assig'norctof'Republic Flow Meters Company; Chicago; Ill.;` al: corporationof -Illinois Application April 28,;1950,SrialgNoalS3,8292 4 This .inventionrelates .to control systemsand j more particularly to an electrically ,operated'syse tem for vvcontrolling ia.. condition simultaneously'v aiecting a Aplurality of ,separate conditions... As

oneexample,A the control system of the. invention may be utilized tocontrol the supply of coinbustion airto a Vsteam generator in response tov the steamiiow. or pressure and tothe composi` tion of the combustionv gas.

One of the objects of the invention is toprovideacontrol system in which a control operationiseiected inv response to the product of two tipliedfby two kVoltage varying devices connected inseries to produce a resultant voltage proportional to the product 'of the effects.

yStillanother object is to provide a control sys-r tem in whichcontrol is eiected jointly in re^ sponse 'to the product of two conditions and the value: of a third condition affecting said two" conditions to regulate the third condition.

The above and other objects and advantages of the.' invention will be more readily Vapparent when read in connection with the accompanyingdrawing, in which-' Thefsingle'iig'ure isa diagrammatic view `of ya' control system Vembodying the V'inventionV :as ape plied to a steam generator.V j

As illustrated; the'system ofthe presentin` vention is -adapted* to control thesupply'of one of the combustion products to `a steam'generator indicated at I0. Fuelmay be" suppliedto the generatorthrough aninlet conduit II, andair foricombustion maybe supplied through an air regulator will' move Vthe kvalve lI5 jointly` in' vre sponseito .theforce of thediaphragm I1 and the force of the spring I9. The diaphragm I1 4is responsive to the rate of supply of air to the generator, and for this purpose its opposite sides are =^connected through pipes l2 I- to the f' opposite sides of an orifice 22 in the air supply conduit.

The spring I9 is adjusted in response to two The Jproducts of combustion' pass fromthe generator through ailue I3, and

3 Claims. (Cl. 236-44) conditions foffoperation` L of th'e i'generator; both of Iwhich are affected 'by the rate of air supply.;

n As' 'shownfthe spring I 9 is vrnovedrby4 a 'reversible' electric motor unit '23' having a movable arm-i23 and which may be of the `type more"particularlyyA described and claimed in my copending applicae tionjSe'rial' No: 943010,*led May-118,1 1949.-'V The unit'tovary th'eitensi'ofn4 of the-'spring I 9 Cis correy trol'led' in *response *to' the phase'andlamplitude of'ithe voltagefsupplied to the motor unit'by ane'- amplier 24:" In the construction illustrated,-' the amplifier-` isi controlled ninE response Ito Variations'v in a' function of`J the steam's' generated 'i in" the -V generator-and tocthe compositionrof-"the com--y bustionfgas'f- 'Io' *measure` the function of fthe steam gener-` ated; ay regulator 2 5 'is provided fhavingfaicontrol diaphragm '2S^connected vto th'esteam header-'fil torrespcnd 1to thee/steam pressure-th`ereina-y The regulator includes a power# operated arme 21 which-is movedto a y@position proportionaltofthes steamy-pressures l The flue gascom'positio'nds measured-by aiflue gas analyzer l28 Aconnectedfto the flue I 3 to `'receivef-gas samples-therefrom.' -The analyzer-:2811 includesanoperating-'arm -29ewhich ismoved-in accordancewith variations in the -compositonfof the uefgas-and whichloads a regulator `3| similar to 'theregulaton 25 .and vhaving a; movable "i power operated output-'arm 32.4` AAs.V shown;-\th"e VAr arm- 29 v"of the flue gasanal-yzer-varie'sthe tension'T of 5a :spring'33 Awhich-'acts as rthefloading element-i for the regulator 3 I Iso thatthe regulatonloutput if arm BZ-willl' move Sto a position:dependentgupont the .tension of 'thelspring 33'; i

According to the presentinvention, :the eiiects;f. of the =zregulatorsa25 and 3I vare-combined'elec-,aA tricallyto 'control' the motor unit 23;thereby to;- vary the -tension of the springIS; -As shownthe. regulatorrarm f 2 'l is connected to. a movable consv f tact Ifor -wiper which is :movable 'overfan-imaVv pedante 'such as` al resistancefSS connectedracrossf.: a source :of 'power suchv as an alternating cur-w rent circuit 36.V` The wiper-34 isconnected toone end of lanimpeda'ncefS'I "also shown asaalrresisty ance; the other endfof-iwhic'hf-is 1 connected .toene sideof th'ef'source-Sii: A movablefwiperllen.-Y gages theriresistance `3 'I- 'and is connected rtoxthe arm 32 of regulator 3I to be shifted therebys. The wiper 38 is connectedto one of fthe-'input terminals of the amplifier `24.

To balance the system" a third`impedancez Yshown asvafresistance 39 is'fconnectedacross the source A-36 land 'has' a movable wiper l4I thereon`r which is'connected 'to thearm 23'v of the motor unit 23 to vbeadjustedtherebyr 'I'he-wiper-flI1 is connected lto thelother-'input terminal rof 'the- With the system in balance, the potentiometer unit formed by the wiper 34 and resistance 35 will develop a voltage which is proportional to the position ,of the regulator arm 21 and is indirectly proportional to the pressureoff steam in the header I4. This voltage will be impressed across the resistance 31, and the wiper 38 will derive from the resistance 31 a second voltage which is determined by the adjustment of the wiper 38. This is, in turn, proportional to the composition of the ue gas, and since the two resistance units are in series, the output voltage between the wiper 38 and the bottom line of the circuit 36 will be proportional vto the products of the values of steam pressure and flue gas composition. With the air supply to the generator at the proper value, the motor unit 23 will have adjusted the Wiper 4|.'so that its voltageis equal and opposite to the voltage at the wiper 38. As a result, the input voltage to the amplifier 24 will be zero, and the system will be stationary.

Upon a changein either the Ysteam pressure or the flue gas composition, one or the other lof the wipers 34 or 38 will be shifted to effect a change in the voltage at' the wiper 38. Since this voltage is no longer equal to that at the wiper 4|, an input voltage will be'supplied to the amplifier 24 whose phase depends upon the direction of displacement of the voltages and whose amplitude is equal to the difference in the voltages. This input voltage will -be amplied and supplied to the motor 23 to vary the tension ofthe spring I9 in an amount and a direction depending upon the direction and amount of deviationof the original condition from balance. At the same time the motor unit 23 will shift the Wiper 4l in a direction to restore the voltage balance and will change in the tension of the spring I9 will cause the regulator I6 to move the valve [to change thel air supply tothe -steam generator in a direction to restore the original condition to its desiredvalue. For, example, upon-a drop in steam pressure the ffair; supply will b e increased,and the supply of-fuelmay be simultaneouslyincreased to increase the rate of combustion, thereby to bring the pressure backA to the desired value. Similarly, if the flue gas analyzer indicatesA an excess amount offree oxygen in the flue gas, the valve l5 willbe closed slightly to reduce the air supply thereby to bring the amount of free oxygen inthe flue gas back to the desired value. As the yair flow increases or decreases, it will change the loading on. the diaphragm l1 to balance the ,changed tension onthe spring 19, therebygto rebalance the'regulator I6. Also, if there shouldy be any change inthe air'supplydue to' some external condition, the diaphragm I1 Will'adjust the regulator I6 to shiftr the valve l5` and bring the air supply back to the desired value. the present system, control of the air to the steam generator is jointly responsive to the rate of air supply and to the producty of factors repre-A sentative of steam pressure and `flue gasV composition. v v v While the invention has been particularlydescribed in connection with thegcontrolof a steam generator, it will beapparent that the principles thereof' might beV appliedto various other types of control operations wherein one condition is to Thus, with 4 otherwise than by the terms of the appended claims.

What is claimed is:

, l. A ,control system comprising an .impedance connected across asource of voltage, an adjustable connection to the impedance to derive a variable voltage therefrom, a regulator responsive to a first condition to adjust the connection, a second impedance connected between the adjustable connection and one side of the source. a second adjustable connection to the second impedance, a second regulator responsive to a second condition to adjust the second connection, a third impedance connected across said source, a third adjustable connection to the third im pedance, control means for a third condition affecting both of the first two named conditions, a regulator connected to the control means to control the third condition, loading means on the regulator .responsive to the third condition, an

electric motor unit responsive to the voltageA between the second and third connections, a connection from the electric motor unit to the third connection to adjust it and a resilient'connection t between the motor means and the regulator to 'I vary the loading of the regulator by the loading means. ,v

2. A control system comprising a first variable electrical device to produce a variable voltage, a iirst regulator responsive to a rst condition to adjustthe first device, a second variable electrical device connected in series with the iirst y device to vary the output voltage of thefrst" device, a second regulator responsive to a second condition to control the second device, a third variable electricaldevice to produce a third variable voltage, control means for a third condition aiiecting both of the rst two named con.-

ditions, and means jointly responsive to the third j condition and-the difference in the voltages produced at the second and third devices to adjust vthe third device and the control means.

3. A combustion control system forV a steam generator comprisingy a first regulator responsive to a function of the steam generated by the boiler, a vfirst variable electrical device adjusted by the regulator to produce a variable voltage,

a second variable electrical device in series with the first device to vary the output voltage of the iirst device, a second regulator responsive j Ato a function of the combustion inthe generator 'to adjust the second device, a third variable electrical device, control means tn .control the supply of an element entering into combustion to the generator, and means jointly! responsiveto the difference in voltages produced at the second and third devices and to the rate of supply be controlled in response'to the-product oftwo- Y` or more other conditions.

be limited to the exact arrangement shown Ynor of said element to adjust the third device and the control means. A

CHARLES H. sMoorr.

REFERENCES CITED V'Ihe' following references are of record in theV file of this patent: Y y l y UNITED STATES PATENTS Number VOTHER REFERENCES E1ectronics,August, 1946, pp. by William Shannon).

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